TY  - JOUR
A1  - Reyes-Pérez, J.
A1  - Morisset, C.
A1  - Pena, M.
A1  - Mesa-Delgado, A.
T1  - A consistent spectral model of WR 136 and its associated bubble NGC 6888
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - We analyse whether a stellar atmosphere model computed with the code CMFGEN provides an optimal description of the stellar observations of WR 136 and simultaneously reproduces the nebular observations of NGC 6888, such as the ionization degree, which is modelled with the pyCloudy code. All the observational material available (far and near UV and optical spectra) were used to constrain such models. We found that the stellar temperature T∗, at τ = 20, can be in a range between 70 000 and 110 000 K, but when using the nebula as an additional restriction, we found that the stellar models with T∗ ∼ 70 000 K represent the best solution for both, the star and the nebula.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88274
SP  - 321
EP  - 324
ER  - 
TY  - JOUR
A1  - Arthur, S. J.
T1  - Wolf-Rayet nebulae and the wind-interstellar medium interaction
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - I review our current understanding of the interaction between a Wolf-Rayet star's fast wind and the surrounding medium, and discuss to what extent the predictions of numerical simulations coincide with multiwavelength observations of Wolf-Rayet nebulae. Through a series of examples, I illustrate how changing the input physics affects the results of the numerical simulations. Finally, I discuss how numerical simulations together with multiwavelength observations of these objects allow us to unpick the previous mass-loss history of massive stars.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88267
SP  - 315
EP  - 320
ER  - 
TY  - JOUR
A1  - Russell, C. M. P.
A1  - Corcoran, M. F.
A1  - Cuadra, J.
A1  - Owocki, S. P.
A1  - Wang, Q. D.
A1  - Hamaguchi, K.
A1  - Sugawara, Y.
A1  - Pollock, A. M. T.
A1  - Kallman, T. R.
T1  - Hydrodynamic and radiative transfer modeling of X-ray emission from colliding WR winds
BT  - WR 140 & the Galactic center
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Colliding Wolf-Rayet (WR) winds produce thermal X-ray emission widely observed by X-ray telescopes. In wide WR+O binaries, such as WR 140, the X-ray flux is tied to the orbital phase, and is a direct probe of the winds’ properties. In the Galactic center, ~30 WRs orbit the super massive black hole (SMBH) within ~10”, leading to a smorgasbord of wind-wind collisions. To model the X-ray emission of WR 140 and the Galactic center, we perform 3D hydrodynamic simulations to trace the complex gaseous flows, and then carry out 3D radiative transfer calculations to compute the variable X-ray spectra. The model WR 140 RXTE light curve matches the data well for all phases except the X-ray minimum associated with periastron, while the model spectra agree with the RXTE hardness ratio and the shape of the Suzaku observations throughout the orbit. The Galactic center model of the Chandra flux and spectral shape match well in the region r ≤ 3”, but the model flux falls off too rapidly beyond this radius.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88255
SP  - 309
EP  - 312
ER  - 
TY  - JOUR
A1  - Gosset, E.
T1  - Studies of WR+O colliding-wind binaries
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Two of the main physical parameters that govern the massive star evolution, the mass and the mass-loss rate, are still poorly determined from the observational point of view. Only binary systems could provide well constrained masses and colliding-wind binaries could bring some constraints on the mass-loss rate. Therefore, colliding-wind binaries turn out to be very promising objects. In this framework, we present detailed studies of basic observational data obtained with the XMM-Newton facility and combined with ground-based observations and other data. We expose the results for two particularly interesting WR+O colliding-wind binaries: WR22 and WR21a.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88247
SP  - 305
EP  - 308
ER  - 
TY  - JOUR
A1  - Huenemoerder, D.
A1  - Gayley, K.
A1  - Hamann, Wolf-Rainer
A1  - Ignace, R.
A1  - Nichols, J.
A1  - Oskinova, Lida
A1  - Pollock, A. M. T.
A1  - Schulz, N.
T1  - High Resolution X-Ray Spectra of WR 6
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - As WR 6 is a putatively single WN4 star, and is relatively bright (V = 6.9), it is an ideal case for studying the wind mechanisms in these extremely luminous stars. To obtain higher resolution spectra at higher energy (above 1 keV) than previously obtained with the XMM/Newton RGS, we have observed WR 6 with the Chandra High Energy Transmission Grating Spectrometer for 450 ks. We have resolved emission lines of S, Si, Mg, Ne, and Fe, which all show a “fin"-shaped prole, characteristic of a self-absorbed uniformly expanding shell. Steep blue edges gives robust maximal expansion velocities of about 2000 km/s, somewhat larger than the 1700km/s derived from UV lines. The He-like lines all indicate that X-ray emitting plasmas are far from the photosphere – even at the higher energies where opacity is lowest { as was also the case for the longer wavelength lines observed with XMM-Newton/RGS. Abundances determined from X-ray spectral modeling indicate enhancements consistent with nucleosynthesis. The star was also variable in X-rays and in simultaneous optical photometry obtained with Chandra aspect camera, but not coherently with the optically known period of 3.765 days.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88236
SP  - 301
EP  - 304
ER  - 
TY  - JOUR
A1  - Oskinova, Lida
T1  - X-ray emission from single WR stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - In this review I briefly summarize our knowledge of the X-ray emission from single WN, WC, and WO stars. These stars have relatively modest X-ray luminosities, typically not exceeding 1L⊙. The analysis of X-ray spectra usually reveals thermal plasma with temperatures reaching a few x10 MK. X-ray variability is detected in some WN stars. At present we don't fully understand how X-ray radiation in produced in WR stars, albeit there are some promising research avenues, such as the presence of CIRs in the winds of some stars. To fully understand WR stars we need to unravel mechanisms of X-ray production in their winds.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88228
SP  - 295
EP  - 300
ER  - 
TY  - JOUR
A1  - Falceta-Goncalves, D.
T1  - Magnetic fields, non-thermal radiation and particle acceleration in colliding winds of WR-O stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Non-thermal emission has been detected in WR-stars for many years at long wavelengths spectral range, in general attributed to synchrotron emission. Two key ingredients are needed to explain such emissions, namely magnetic fields and relativistic particles. Particles can be accelerated to relativistic speeds by Fermi processes at strong shocks. Therefore, strong synchrotron emission is usually attributed to WR binarity. The magnetic field may also be amplified at shocks, however the actual picture of the magnetic field geometry, intensity, and its role on the acceleration of particles at WR binary systems is still unclear. In this work we discuss the recent developments in MHD modelling of wind-wind collision regions by means of numerical simulations, and the coupled particle acceleration processes related.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88211
SP  - 289
EP  - 292
ER  - 
TY  - JOUR
A1  - Mohamed, S.
A1  - Mackey, J.
A1  - Langer, N.
A1  - Podsiadlowski, Philipp
T1  - Shaping the outflows of Wolf-Rayet stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Wolf-Rayet (WR) stars lose copious amounts of mass and momentum through dense stellar winds. The interaction of these outflows with their surroundings results in highly structured and complex circumstellar environments, often featuring knots, arcs, shells and spirals. Recent improvements in computational power and techniques have led to the development of detailed, multi-dimensional simulations that have given new insight into the origin of these structures, and better understanding of the physical mechanisms driving their formation. We review three of the main mechanisms that shape the outflows of WR stars:
• interaction with the interstellar medium (ISM), i.e., wind-ISM interactions;
• interaction with a stellar wind, either from a previous phase of evolution or the wind from a companion star, i.e., wind-wind interactions;
• and interaction with a companion star that has a weak or insignificant outflow (e.g., a compact companion such as a neutron star or black hole), i.e.,wind-companion interactions.
We also highlight the broader implications and impact of these circumstellar structures for related phenomena, e.g., for X-ray binaries and Gamma-ray bursts.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88200
SP  - 283
EP  - 288
ER  - 
TY  - JOUR
A1  - Hendrix, T.
A1  - Keppens, R.
T1  - Modelling colliding wind binaries in 2D
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - We look at how the dynamics of colliding wind binaries (CWB) can be investigated in 2D, and how several parameters influence the dynamics of the small scale structures inside the colliding wind and the shocked regions, as well as in how the dynamics influence the shape of the collision region at large distances. The parameters we adopt are based on the binary system WR98a, one of the few Wolf-Rayet (WR) dusty pinwheels known.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88198
SP  - 279
EP  - 282
ER  - 
TY  - JOUR
A1  - Williams, P. M.
A1  - van der Hucht, K. A.
T1  - The colliding-wind WC9+OB system WR 65 and dust formation by WR stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Observations of the WC9+OB system WR65 in the infrared show variations of its dust emission consistent with a period near 4.8 yr, suggesting formation in a colliding-wind binary (CWB) having an elliptical orbit. If we adopt the IR maximum as zero phase, the times of X-ray maximum count and minimum extinction to the hard component measured by Oskinova & Hamann fall at phases 0.4–0.5, when the separation of the WC9 and OB stars is greatest. We consider WR65 in the context of other WC8–9+OB stars showing dust emission.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88188
SP  - 275
EP  - 278
ER  - 
TY  - JOUR
A1  - Cherchneff, I.
T1  - Dust formation in carbon-rich Wolf-Rayet colliding winds
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Carbon-rich Wolf-Rayet stars are efficient carbon dust makers. Despite the strong evidence for dust formation in these objects provided by infrared thermal emission from dust, the routes to nucleation and condensation and the physical conditions required for dust production are still poorly understood. We discuss here the potential routes to carbon dust and the possible locations conducive to dust formation in the colliding winds of WC binaries.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88177
SP  - 269
EP  - 274
ER  - 
TY  - JOUR
A1  - Guerrero, Martín A.
T1  - Planetary nebulae and Their Central Stars in X-rays
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Two types of X-ray sources are mostly found in planetary nebulae (PNe): point sources at their central stars and diffuse emission inside hot bubbles. Here we describe these two types of sources based on the most recent observations obtained in the framework of the Chandra Planetary Nebula Survey, ChanPlaNS, an X-ray survey targeting a volume-limited sample of PNe. Diffuse X-ray emission is found preferentially in young PNe with sharp, closed inner
shells. Point sources of X-ray emission at the central stars reveal magnetically active binary companions and shock-in stellar winds.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88160
SP  - 263
EP  - 266
ER  - 
TY  - JOUR
A1  - Miszalski, B.
A1  - Manick, R.
A1  - McBride, V.
T1  - Post-common-envelope Wolf-Rayet central stars of planetary nebulae
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Nearly 50 post-common-envelope (post-CE) close binary central stars of planetary nebulae (CSPNe) are now known. Most contain either main sequence or white dwarf (WD) companions that orbit the WD primary in around 0.1–1.0 days. Only PN G222.8–04.2 and NGC 5189 have post-CE CSPNe with a Wolf-Rayet star primary (denoted [WR]), the low-mass analogues of massive Wolf-Rayet stars. It is not well understood how H-deficient [WR] CSPNe form, even though they are relatively common, appearing in over 100 PNe. The discovery and characterisation of post-CE [WR] CSPNe is essential to determine whether proposed binary formation scenarios are feasible to explain this enigmatic class of stars. The existence of post-CE [WR] binaries alone suggests binary mergers are not necessarily a pathway to form [WR] stars. Here we give an overview of the initial results of a radial velocity monitoring programme of [WR] CSPNe to search for new binaries. We discuss the motivation for the survey and the associated strong selection effects. The mass functions determined for PN G222.8–04.2 and NGC 5189, together with literature photometric variability data of other [WR] CSPNe, suggest that of the post-CE [WR] CSPNe yet to be found, most will have WD or subdwarf O/B-type companions in wider orbits than typical post-CE CSPNe (several days or months c.f. less than a day).
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88156
SP  - 259
EP  - 262
ER  - 
TY  - JOUR
A1  - Todt, Helge Tobias
A1  - Hamann, Wolf-Rainer
T1  - Wolf-Rayet central stars of planetary nebulae
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - A significant number of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient, showing a chemical composition of helium, carbon, and oxygen. Most of them exhibit Wolf-Rayet-like emission line spectra, similar to those of the massive WC Pop I stars, and are therefore classified as of spectral type [WC]. In the last years, CSPNe of other Wolf-Rayet spectral subtypes have been identified, namely PB 8, which is of spectral type [WN/C], and IC 4663 and Abell 48, which are of spectral type [WN]. We review spectral analyses of Wolf-Rayet type central stars of different evolutionary stages and discuss the results in the context of stellar evolution. Especially we consider the question of a common evolutionary channel for [WC] stars. The constraints on the formation of [WN] or [WC/N] subtype stars will also be addressed.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88147
SP  - 253
EP  - 258
ER  - 
TY  - JOUR
A1  - Dessart, L.
T1  - Wolf-Rayet stars as supernova progenitors
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - In this review, I discuss the suitability of massive star progenitors, evolved in isolation or in interacting binaries, for the production of observed supernovae (SNe) IIb, Ib, Ic. These SN types can be explained through variations in composition. The critical need of non-thermal effects to produce He I lines favours low-mass He-rich ejecta (in which ^56 Ni can be more easily mixed with He) for the production of SNe IIb/Ib, which thus may arise preferentially from moderate-mass donors in interacting binaries. SNe Ic may instead arise from higher mass progenitors, He-poor or not, because their larger CO cores prevent efficient non-thermal excitation of He i lines. However, current single star evolution models tend to produce Wolf-Rayet (WR) stars at death that have a final mass of > 10 M⊙. Single WR star explosion models produce ejecta that are too massive to match the observed light curve widths and rise times of SNe IIb/Ib/Ic, unless their kinetic energy is systematically and far greater than the canonical value of 10^56 erg. Future work is needed to evaluate the energy/mass degeneracy in light curve properties. Alternatively, a greater mass loss during the WR phase, perhaps in the form of eruptions, as evidenced in SNe Ibn, may reduce the final WR mass. If viable, such explosions would nonetheless favour a SN Ic, not a Ib.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88133
SP  - 245
EP  - 250
ER  - 
TY  - JOUR
A1  - Langer, N.
A1  - Sanyal, D.
A1  - Grassitelli, L.
A1  - Szésci, D.
T1  - The stellar Eddington limit
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - It is often assumed that when stars reach their Eddington limit, strong outflows are initiated, and that this happens only for extreme stellar masses. We discuss here that in models of up to 500 M⊙, the Eddington limit is never reached at the stellar surface. Instead, we argue that the Eddington limit is reached inside the stellar envelope in hydrogen-rich stars above ∼ 30 M⊙ and in Wolf-Rayet stars above ∼ 7 M⊙, with drastic effects for their struture and stability.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88121
SP  - 241
EP  - 244
ER  - 
TY  - JOUR
A1  - Groh, J. H.
T1  - The end stages of massive star evolution
BT  - WR stars as SN Ibc progenitors
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - The morphological appearance of massive stars across their post-Main Sequence evolution and before the SN event is very uncertain, both from a theoretical and observational perspective. We recently developed coupled stellar evolution and atmospheric modeling of stars done with the Geneva and CMFGEN codes, for initial masses between 9 and 120 M⊙. We are able to predict the observables such as the high-resolution spectrum and broadband photometry. Here I discuss how the spectrum of a massive star changes across its evolution and before death, with focus on the WR stage. Our models indicate that single stars with initial masses larger than 30 M⊙ end their lives as WR stars. Depending on rotation, the spectrum of the star can either be that of a WN or WO subtype at the pre-SN stage. Our models allow, for the first time, direct comparison between predictions from stellar evolution models and observations of SN progenitors.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88115
SP  - 237
EP  - 240
ER  - 
TY  - JOUR
A1  - Wofford, A.
A1  - Charlot, S.
A1  - Eldridge, J. J.
T1  - Properties of LEGUS Clusters Obtained with Different Massive-Star Evolutionary Tracks
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - We compute spectral libraries for populations of coeval stars using state-of-the-art massive-star evolutionary tracks that account for different astrophysics including rotation and close-binarity. Our synthetic spectra account for stellar and nebular contributions. We use our models to obtain E(B – V ), age, and mass for six clusters in spiral galaxy NGC 1566, which have ages of < 50 Myr and masses of > 5 x 104M⊙ according to standard models. NGC 1566 was observed from the NUV to the I-band as part of the imaging Treasury HST program LEGUS: Legacy Extragalactic UV Survey. We aim to establish i) if the models provide reasonable fits to the data, ii) how well the models and photometry are able to constrain the cluster properties, and iii) how different the properties obtained with different models are.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88109
SP  - 233
EP  - 236
ER  - 
TY  - JOUR
A1  - Georgy, C.
A1  - Ekström, S.
A1  - Hirschi, R.
A1  - Meynet, G.
A1  - Groh, J. H.
A1  - Eggenberger, P.
T1  - Wolf-Rayet stars as an evolved stage of stellar life
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - Wolf-Rayet (WR) stars, as they are advanced stages of the life of massive stars, provide a good test for various physical processes involved in the modelling of massive stars, such as rotation and mass loss. In this paper, we show the outputs of the latest grids of single massive stars computed with the Geneva stellar evolution code, and compare them with some observations. We present a short discussion on the shortcomings of single stars models and we also briefly discuss the impact of binarity on the WR populations.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88097
SP  - 229
EP  - 232
ER  - 
TY  - JOUR
A1  - Munoz, M.
A1  - Moffat, Anthony F. J.
A1  - Hill, G. M.
A1  - Richardson, N. D.
A1  - Pablo, H.
T1  - The missing Wolf-Rayet X-ray binary systems
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - We investigate the rarity of the Wolf-Rayet X-ray binaries (WRXRBs) in contrast to their predecessors, the high mass X-ray binaries (HMXRBs). Recent studies suggest that common envelope (CE) mergers during the evolution of a HMXRBs may be responsible (Linden et al. 2012). We conduct a binary population synthesis to generate a population of HMXRBs mimicking the Galactic sample and vary the efficiency parameter during the CE phase to match the current WRXRB to HMXRB ratio. We find that ∼50% of systems must merge to match observational constraints.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88082
SP  - 225
EP  - 228
ER  -